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Armstrong type ceiling bass trap - practical questions
Old 5th October 2019
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Armstrong type ceiling bass trap - practical questions

Hello to everyone.

I'm currently packing small truck of mineral wool into small room and everything is going more or less well, but there are some questions regarding ceiling construction.

I've already have 12" lowered framing for Armstrong type ceiling, tiles are Rockfon Industrial 1" (GFR 21700 AFAIR) and filling is fluffy Knauf Ecose plates.
Prediction of porous absorber calculator is quite nice, and if i assume 2,2 kg/sq.m Rockfon tiles as membrane absorber (why not?) its Fc shall be around 62 Hz which is even better.

Right now on FR and waterfall i still have predicted issues with floor-ceiling mode - 65, 130, 195 Hz, just because ceiling is not assembled completely yet.

But to prevent time-consuming errors, i'd be glad to know

1) shall i fight only vertical mode with ceiling construction or it's better to keep in mind other modes also?
In principle I can try to go little lower (i.e. 2 layers of tiles, more membrane mass and higher GFR of outer layer) but i'm not sure if that really required. Especially if pressure zone in my room ends at 37 Hz ...

2) how do you think, is full tight packing of ceiling cavity with fluffy wool really crucial for its efficiency?
I can use bigger packs (24" wide) and fill almost all room, but i'll have to remove part of hangers (they are sharp and cut packs when i put them in), or use 12" wide packs, and more free space will be left (somewhere over tiles will be just air gap).

I'm not sure if 4 cubical meters of fluffy Knauf will perform much better than 2 or 3, but if that will SERIOUSLY affect absorption below 100 Hz, i'll prefer more absorption. Otherwise I'd prefer safety.

3)If there are better combination of hard mineral wool tiles and fluffy mineral wool than just 1" of hard and 12" of fluffy, i'm all ears.
In principle, I have a lot of both ...
Player for a while with porpous absorber calculator and there's no single better solution - or we go deeper, or we go more efficient around 100 Hz ...

Thank you in advance
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